Poly(aryl ether ketone) polymers (i.e., PAEK polymers) are a well known class of engineering polymers useful in various fields of endeavor whose structures combine both ether and ketone groups. Poly(etheretherketone) (PEEK) and poly(etherketone) (PEK) are the most common PAEK. PEK and PEEK are high-strength, radiation-resistant engineering plastics, thermally stable and highly resistant to chemicals.
Processes for preparing these polymers can be found in, e.g., U.S. Pat. Nos. 3,953,400, 3,956,240, 3,928,295, and 4,176,222, all incorporated herein by reference. Generally, PAEK polymers are prepared by aromatic nucleophilic substitution. For example, a bisphenol can be used as a nucleophilic component which is deprotonated with a base such as NaOH, Na2CO3 or K2CO3. The resultant bisphenolate may then react with a bishalogenated monomer, e.g., a dihalobenzophenone such as difluorobenzophenone to form PEEK via nucleophilic substitution, with the halogen atoms of the dihalobenzophenone acting as leaving groups. For high temperature processes (i.e. requiring reaction temperatures higher than 250° C., more particularly more than 300° C.), fluorine is the preferred halogen. Examples of fluorinated monomers are represented by structures 1 to 6 (4,4′-difluorobenzophenone (1), 1,4-bis(4′-fluorobenzoyl)benzene (2), 1,3- bis(4′-fluorobenzoyl)benzene (3), etc). Often, such PAEK reactions are carried out in a solvent that is, or that contains, diphenyl sulfone (DPS). For such high temperature processes, a high purity of solvent is required.

To the best of the inventor's knowledge, only two documents pertain to the recovery of diphenyl sulfone in a polyether manufacturing process. In JP 2004/315764, diphenyl sulfone is recovered by precipitation. Besides, a low boiling organic solvent or a mixture of a low boiling organic solvent with water (homo- or heteroazeotrope) on one hand, and water on the other hand are recovered successively by distillation.
In JP 2007/238890, the addition of water is used to help remove low boiling solvent. The presence of high levels of inorganic salts increases the risk of corrosion of the equipment, especially at the high temperatures.
Because the most economically viable processes for manufacturing PAEKs typically involve a recycling of the reaction solvent comprising, consisting essentially of, or consisting of DPS, and given the difficulties of high temperature recovery/distillation/purification of DPS, a low temperature recovery operation (e.g., <150° C., preferably <70° C., more preferably below 65° C.), which preferably does not involve distillation of the DPS and which provides DPS of high purity is highly desirable.